What Is NC Machining?- Definition and Basic Guide

What is NC Machining?

Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, and 3D printers) by means of a computer.

A CNC machine processes a piece of material (metal, plastic, wood, ceramic, or composite) to meet specifications by following a coded programmed instruction and without a manual operator directly controlling the machining operation.

A CNC machine is a motorized maneuverable tool and often a motorized maneuverable platform, which are both controlled by a computer, according to specific input instructions.

Instructions are delivered to a CNC machine in the form of a sequential program of machine control instructions such as G-code and M-code, then executed.

The program can be written by a person or, far more often, generated by graphical computer-aided design (CAD) software and/or computer-aided manufacturing (CAM) software.

In the case of 3D printers, the part to be printed is “sliced”, before the instructions (or the program) are generated. 3D printers also use G-Code.

CNC is a vast improvement over non-computerized machining that must be manually controlled (e.g. using devices such as hand wheels or levers) or mechanically controlled by pre-fabricated pattern guides (cams).

In modern CNC systems, the design of a mechanical part and its manufacturing program is highly automated.

The part’s mechanical dimensions are defined using CAD software and then translated into manufacturing directives by computer-aided manufacturing (CAM) software.

The resulting directives are transformed (by “post processor” software) into the specific commands necessary for a particular machine to produce the component and then are loaded into the CNC machine.

Since any particular component might require the use of a number of different tools – drills, saws, etc. – modern machines often combine multiple tools into a single “cell”.

In other installations, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine.

In either case, the series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD drawing.

What is NC machine?

Numerical control is defined as the form of programmable automation in which numbers letters and symbols control the operation.

This instruction is designed to do a particular job. NC machines have the capability to change the program for each job i.e. when the job changes the program instruction is also changed.

It is easier to change the program instruction than to modify the production equipment. This flexibility reduces the overall production cost.

How Does NC Machining Work?

NC machining, or Numerical Control machining, operates through a series of precise steps, each controlled by pre-programmed instructions.

This process allows for the automated and accurate control of machine tools, resulting in consistent and high-quality production.

Let’s break down the main stages of the NC machining process to understand how it works:

#1. Programming the Machine.

The first step in NC machining involves programming the machine with specific instructions.

These instructions, often in the form of G codes and M codes, tell the machine how to perform the required operations.

This programming can be done using computer-aided design (CAD) and computer-aided manufacturing (CAM) software, ensuring precision in the commands given to the machine.

#2. Setting Up the Machine Tool.

Once the program is ready, the machine tool is set up. This involves installing the necessary cutting tools and securing the workpiece in place.

The setup must be accurate to ensure that the machining process proceeds smoothly and the final product meets the desired specifications.

#3. Executing the Machining Operation.

With the program loaded and the machine set up, the machining operation can begin.

The NC machine follows the programmed instructions to perform tasks such as drilling, milling, or cutting.

Each movement and operation is controlled by the pre-defined instructions, allowing for high precision and repeatability.

#4. Inspecting the Final Product.

After the machining operation is complete, the final product is inspected to ensure it meets the required standards.

This inspection can involve measuring the dimensions of the part, checking for any defects, and verifying that the part matches the specifications provided in the design.

What are the Key Components of an NC Machine?

Understanding the key components of an NC machine is essential for grasping how these machines function and differ from their more advanced counterpart, CNC (Computer Numerical Control) machines.

#1. Controller.

The controller is the central part of an NC machine, often referred to as the brain of the machine. It processes the input instructions and directs the machine tools to perform the desired operations.

In CNC machines, this component is more advanced, capable of handling complex algorithms and real-time data processing.

#2. Machine Tools.

These include various tools such as drills, lathes, and mills, which perform the actual machining operations.

The tools are attached to the machine and move according to the instructions from the controller.

In CNC machines, the range and flexibility of machine tools are greater, allowing for more intricate and precise machining operations.

#3. Input Devices.

Traditional NC machines used punched tapes to input instructions, which are sequences of codes that the machine reads and executes.

Modern CNC machines, however, use digital input methods, such as computer-aided design (CAD) files and computer-aided manufacturing (CAM) software, providing more versatility and ease of use.

#4. Servo Motors.

These motors control the movement of the machine tools, ensuring precision and accuracy. They receive signals from the controller and move the tools to the correct positions.

CNC machines also use servo motors, but with enhanced capabilities for smoother and faster movements.

#5. Feedback Systems.

Feedback systems monitor the operations and ensure the machine tools are performing as instructed.

These systems provide data back to the controller, which can make real-time adjustments to maintain accuracy.

In CNC machines, feedback systems are more sophisticated, offering higher precision and better control over the machining process.

What Controls the Movements of NC Machines?

The movements of NC machines are controlled by a combination of hardware and software components designed to follow pre-programmed instructions accurately.

• Control Unit: The control unit is the brain of the NC machine. It reads the programmed instructions, which are typically written in G code, and converts them into signals that control the machine’s movements.
• Servo Motors: These motors receive signals from the control unit and move the machine tools to the desired positions. Servo motors are essential for precise control of speed and position.
• Feedback Systems: Feedback systems, including encoders and sensors, provide real-time data on the position and movement of machine components. This information is sent back to the control unit, which adjusts operations to maintain accuracy.

What Types of Sensors Are Used in NC Machines?

Sensors play a crucial role in ensuring the accuracy and efficiency of NC machines by providing real-time data for adaptive control and feedback systems.

• Position Sensors: These include encoders and resolvers, which monitor the position of machine components, ensuring precise movements.
• Force Sensors: Force sensors measure the cutting force and ensure it stays within optimal limits to prevent tool damage and maintain machining quality.
• Temperature Sensors: These sensors monitor the temperature of machine components and the workpiece, allowing adjustments to prevent overheating and ensure consistent material properties.
• Vibration Sensors: Vibration sensors detect excessive vibrations that could affect machining accuracy and tool life, enabling the machine to adjust parameters to minimize vibrations.

Types of NC Machine

NC (Numerical Control) machines come in various types, each designed for specific applications and machining processes.

Understanding these types helps in selecting the right machine for a particular manufacturing task.

#1. Point-to-Point (PTP) Machines

These machines perform movements from one discrete point to another. They are ideal for tasks such as drilling, spot welding, and punching where the tool needs to move to a specific location, perform an operation, and then move to another location.

The key characteristic of PTP machines is their ability to precisely control the position of the tool, ensuring high accuracy in operations.

#2. Continuous Path (Contouring) Machines.

These machines are designed to perform complex and continuous movements along a defined path.

Unlike Point-to-Point (PTP) machines, which move from one discrete point to another, contouring machines can move simultaneously along multiple axes.

This allows them to create intricate and smooth surfaces, making them ideal for operations such as milling and complex cutting tasks.

#3. Dedicated Machines.

These machines are specialized for specific tasks and are not as versatile as other types.

They are designed for high efficiency in performing repetitive operations and are commonly used in mass production environments.

Examples include specific machines for drilling, boring, or cutting, which are optimized to perform these tasks with high speed and accuracy.

#4. Modular Machines.

These machines are designed with flexibility in mind, allowing manufacturers to customize and adapt the machine to different tasks by adding or removing modules.

This modularity makes them highly versatile and suitable for various machining operations.

#5. Adaptive Control Machines.

These machines automatically adjust their operating parameters based on real-time feedback.

This adaptability allows for higher precision and efficiency, as the machine can respond to changes in the machining environment and optimize its performance accordingly.

Types of NC Systems

NC (Numerical Control) systems have evolved to meet various manufacturing needs, providing precision and automation across different applications.

Understanding the different types of NC systems helps in selecting the appropriate system for specific tasks.

#1. Point-to-Point (PTP) Systems.

These systems are designed to move the machine tool from one discrete point to another, stopping at each point to perform a specific operation.

PTP systems are highly efficient for tasks that require precise positioning but do not involve continuous motion along a path.

Applications:

• Drilling: PTP systems are widely used in drilling operations where precise hole placement is critical.
• Spot Welding: These systems are perfect for spot welding, which requires the tool to move to specific points on the workpiece.
• Component Insertion: PTP systems are suitable for automated assembly processes, where components need to be placed at precise locations.

#2. Contouring Systems.

Contouring, or continuous path, systems are designed to follow complex, continuous paths rather than moving from one discrete point to another.

These systems are ideal for operations that require the machine tool to move smoothly along a predetermined path, such as milling and engraving.

Applications:

• Milling: Ideal for milling operations that require the tool to follow a continuous path to create complex shapes.
• Engraving: Perfect for engraving detailed designs on various materials, ensuring smooth and precise movements.
• Mold Making: Used in mold making to create intricate and precise molds for manufacturing.

#3. Closed-Loop Systems.

These systems use feedback from sensors to continuously monitor and adjust the machine’s operations.

The feedback ensures that the machine maintains high precision and corrects any deviations in real-time.

Applications:

• Precision Machining: Suitable for tasks that require high precision and accuracy, such as aerospace and medical device manufacturing.
• Complex Operations: Ideal for complex machining operations that demand continuous monitoring and adjustments to maintain quality.
• Quality Control: Used in applications where maintaining consistent quality is critical, ensuring that each part meets exact specifications.

#4. Open-Loop Systems.

These systems operate without feedback, meaning they follow pre-set instructions without adjusting based on real-time data.

Open-loop systems are straightforward and cost-effective, suitable for operations where precise feedback control is not crucial.

Applications:

• Basic Machining Operations: Suitable for tasks that do not require high precision, such as simple drilling or cutting operations.
• Educational Use: Often used in educational settings to teach the basics of NC machining without the complexity of feedback systems.
• Low-Cost Manufacturing: Ideal for manufacturing environments where cost is a critical factor and the required precision is within acceptable limits.

Difference Between NC and CNC Machine

Numerical Control (NC) and Computer Numerical Control (CNC) machining are both processes that use computer networks to control machine tools.

You’ve heard both of them, but you might be wondering what is the difference between NC vs CNC machines.

In short, NC machining is typically used for simpler applications, while CNC machining is used for more complex applications.

NC machines are operated by a set of coded instructions that tell the machine what operations to perform. These instructions are known as G-codes.

CNC machines, on the other hand, are operated by a set of computer-generated instructions known as programs. These programs can be created using a CAM (Computer-Aided Manufacturing) system.

NC vs CNC Machine

Numerical Control (NC)	Computer Numerical Control (CNC)
Stands for Numerical Control.	Stands for Computer Numerical Control.
Uses punch tapes and punch cards for input.	Uses keyboards for input.
Alteration in operation parameters is not possible.	Alteration in operation parameters is possible.
No memory for storing instructions.	Memory exists to store instructions.
Less expensive than CNC.	More expensive than NC.
Maintenance cost is low.	Maintenance cost is high.
Requires highly skilled operators.	Requires less skilled operators.
Less flexible than CNC.	More flexible than NC.
Less accurate than CNC.	High accuracy.
Execution of jobs takes more time.	Execution of jobs takes less time.
Cannot run continuously.	Can run continuously for 24 hours a day.
Limited machine control.	Advanced machine control capabilities.
Programming changes are difficult.	Easy to update and modify programming.
Limited to a basic set of instructions.	Can execute a complex set of instructions.
Lower precision.	High precision in operations.
Less capability for intricate tasks.	Greater capability for intricate and complex tasks.

Applications of numerical control technology

Numerical control technology has application in a wide variety of production operations such as metal cutting, automatic drafting, spot welding, press working, assembly, inspection, etc.

However, NC finds its principal application in metal machining operations. It is built to do virtually the entire metal removing process. (Example for metalworking Turning, sawing, Grinding, Milling, Drilling, boring).

The production jobs where the numerical control machines are most appropriate are listed below.

• The NC technology is suitable to sequence/series of machining process.
• Job geometry is complex, expensive. Mistakes in the process lead to high loss.
• It is expected engineering design changes in future.
• High metal removal is required.
• The work part required 100% inspection.
• There must be close tolerance on work part.
• When many operations need to be done when processing. It is frequently processed in batches of small lot sizes.

Advantages of NC Machine

• Greater manufacturing flexibility. NC can easily adapt to the engineering design changes and a shift in the production schedule.
• Reduced manufacturing lead time. The job can easily and quickly set up with NC.
• Reduced non-productive time. In case of complex machining NC seems helpful to reduce the non-productive time. Because of quick/ automatic tool changing, quick setting up, and reduced workpiece handling time.
• Reduced fixturing. The fixture required in NC operation are simpler and less costly because NC tape does position instead of jig and fixture.
• Reduced inventory. This is the result of fewer setup reduced lead time.
• Quality control improved. No risk of human mistakes. It produces the part with high accuracy. It also reduces the man-hour for inspection.
• Greater operator safety.
• Reduce the scrap. the high accuracy of NC machine helps to reduce scrap material.
• Reduced floor space requirement. since the one NC can do variety of operation it replaces several conventional machines.

Disadvantages of NC Machine

• High investment cost and Maintenance cost. Most complex and sophisticated technology cost more than the conventional machine.
• Require skilled operator. Finding and training of NC personnel should be considered.
• Tearing and wearing of punch tape and less reliable punch tape component.
• Part programming mistake in punched tape.
• No optimal feed and speed. Conventional NC machine do not provide an option to change the cutting speed and feed during the operation.

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